In the technology industry's race to build an online version of pay television, Sony Corp. just took the lead.

The Japanese company has reached a preliminary deal with Viacom Inc. to carry the media giant's channels, such as MTV, Comedy Central and Nickelodeon, on its planned pay-TV service, people familiar with the matter said. None of the other companies vying to launch Internet-based pay TV, including Intel Corp. and Google Inc.,...